Often, in the production of crude oil, steam needs to be injected into the petroleum reservoir because the crude oil is too viscous. Two parameters are usually required to describe a wet, saturated steam flow in a conduit--the total flow rate and the steam quality. The steam quality is defined as the mass fraction of the vapor phase in steam. Once the steam quality is known, properties such as specific volume and enthalpy can be calculated for a given saturation temperature or pressure.
In the current practice of steam metering, two measuring devices are usually needed to obtain the flow rate and steam quality. For example, U.S Pat. No. 4,753,106 by Brenner et al. discloses using an orifice meter to measure the flow rate and a densitometer to measure the density, hence to deduce the quality. U.S. Pat. No. 4,681,466 by Chien et al. discloses a method using two flow meters, but that method is sometimes less than successful because it is based on empirical correlations of flow measurements. U.S. Pat. No. 4,712,006 by Zemel et al. and U.S. Pat. No. 4,645,635 by Yuen et al. both disclose using radioactive elements to measure density, hence quality, but those methods are not easy to apply. Brenner et al., Chien et al., Zemel et al., and Yuen et al. are hereby incorporated by reference for all purposes.